1. Field of the Invention
Embodiments relate to a zoom lens suitable for an imaging device employed in a miniature digital camera, a digital video camera, a mobile phone, a personal digital assistant (PDA), or the like.
2. Description of the Related Art
Recently, distribution of image forming optical devices, such as digital cameras or digital camcoders that use an image pickup device like a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS), is rapidly expanding. Accordingly, a zoom lens that is highly efficient, small, and light is required.
Also, an exchangeable lens camera, wherein a user may exchange lenses according to a photographing purpose, is typically required to have excellent optical performance with a compact size to be easily carried.
In order to manufacture a camera having a compact size, a driving unit such as a motor for auto focusing (AF), may be removed from a camera body, and a function of the driving unit may be installed in an exchangeable lens. In this case, a size of the exchangeable lens is increased and so as to counterbalance the increased size of the exchangeable lens due to the driving unit, it is important to design the lens itself to perform AF with a small driving source. Thus, an AF lens group is desired to be miniaturized and light-weighted in terms of an optical design.
Generally, when a distance of an object changes from an infinity to a short distance, AF is performed by using a first lens group that is capable of obtaining an excellent optical performance in the entire distance of the object. However, lenses included in the first lens group typically have large diameters and are heavy, and thus it is difficult to perform the AF by using a small driving source.
Even a conventional inner focus method, which does not use the first lens group in performing AF, uses too many lenses in an AF optical system, and thus it is difficult to maintain a low price and a compact size of a camera.